Stabilized polyphenylene oxide composition



United States Patent 3,379,875 STABILIZED POLYPHENYLENE OXIDE COMPOSITION Klaus E. Holoch, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York No Drawing. Filed Feb. 21, 1966, Ser. No. 528,784 6 Claims. (Cl. 260-458) ABSTRACT OF THE DISCLOSURE A stabilized polyphenylene oxide composition consisting a polyphenylene oxide and a member selected from the group consisting of the benzoates of Z-mercaptobenzimidazole, Z-mercaptobenzoxazole, and Z-mercaptobenzothiazole.

This invention relates to stabilized polyphenylene oxide comprising a polyphenylene oxide and a member selected from a group consisting of the benzoates of Z-mercaptobenzimidazole, Z-mercaptobenzoxazole, Z-mercaptobenzothiazole.

The polyphenylene oxides are disclosed and claimed in US. Patents Ser. Nos. 3,306,874 and 3,306,875 of Allan S'. Hay the contents of which are incorporated herein by reference. They are characterized by a unique combination of mechanical, chemical and electrical properties over a broad range of temperatures which render them suitable for a wide variety of commercial applications.

Though the polyphenylene oxides possess an outstanding combination of properties their use has been somewhat limited due to marginal aging stability. Heretofore, exposure of the polyphenylene oxides containing at least one aliphatic side chain to oxygen, particularly at elevated temperatures for sustained periods of time cause various reactions to occur within the polymer resulting in discoloration and embrittlement.

In French Patent No. 1,305,508 granted Mar. 18, 1963, Z-mercapto imidiazoles and Z-mercapto thiazoles are disclosed as stabilizers for linear thermoplastics. These materials were used in an attempt to stabilize the polyphenylene oxides and some improvement in stability was observed. However, it has now been unexpectedly found that far better stability can be obtained when the stabilizer is a member selected from the group consisting of benzoates of Z-mercapto imidiazole, Z-mercapto thiazole and Z-mercapto oxazole. It has also been discovered that these benzoates can be formed in situ in the polymer during processing it the mercapto compound is added to the polymer together with a second material capable of reacting therewith during processing to form the benzoate. By using the stabilizer system of this invention with a polyphenylene oxide, it is possible to formulate a polymeric composition having excellent stability to discoloration and embrittlement upon exposure to oxygen at both room and elevated temperatures.

The polyphenylene oxide, as used throughout this disclosure and in the claims is meant to include those polymers described and claimed in the above noted US. patent applications of Allan S. Hay wherein the phenylene nucleus contains at least one aliphatic side chain. The preferred class of polymers in accordance with the present invention are those formed from 2,6 disubstituted phenols 3,379,875 Patented Apr. 23, 1968 and the most preferred polymers are those formed from wherein a is a whole number equal to 0 or 1; Z is a member selected from the group consisting of oxygen, sulfur and nitrogen; and R is a member selected from the group consisting of hydrogen and a benzoyl radical of the following formula:

wherein R" is a member selected from the group consisting of hydrogen and an alkyl group having from 1 to 3 carbon atoms; and b is a whole number equal to from 0 to the number of replaceable hydrogen atoms on the phenylene nucleus; provided that at least one of said R be a benzoyl radical, and provided further that when Z is oxygen or sulfur, a is 0.

For brevity, the expression benzoate will be used throughout the remainder of the disclosure to represent those compounds falling within the scope of Formula I above.

As noted above, the benzoate of the mercapto compound may be used or may be formed in situ by reaction of the mercapto compound with a material capable of forming the benzoate during processing of the polymer. The preferred material for in situ formation is benzoic anhydride. Other compounds include, but are not limited to methyl benzoate, ethyl benzoate, benzoic acid, etc.

There are various methods for forming the stabilized resins of this invention, though the particular method used does not constitute a part of this invention. One procedure involves blending where the stabilizer is added to the other ingredients of the formulation to produce a free flowing, powdery mixture called a dry blend Or a powder blend. Generally, when the stabilizer is in liquid form, it is sprayed on the powdered resin which is stirred in a heated chamber. The stabilizer can be heated prior to spray mixing to reduce the time required to produce the dry blend. Cooling the batch is the final step in producing the dry blend from which it can be fed to an extruder, roll mill or internal type mixer such as the Banbury. Another method comprises the use of diflferential two speed roll mills and internal type mixers. These mixers apply heat and energy to the resin and stabilizer to achieve admixture of the two and produce a powder mass. This can then be fed to the finishing machine, such as a calender to obtain the desired product. A third procedure involves mixing a stabilizer in liquid form with the polymer in powder form. The result is a resin stabilizer suspension which can be stored and ultimately processed by a variety of methods. It can be rotationally cast or slush molded or applied to various substrates such as fabrics, metal and paper by knife coating or spraying. A fourth 3 4 method for incorporating the stabilizer in the polypheuylaluminum foil usin 10 mil shims. Molding temperature ene oxide involves solution techniques. Here the resins was maintained at approximately 550 F. and molding and stabilizers are both dissolved in a mutual solvent time was approximately 2 minutes. The resulting films which is thereafter allowed to evaporate leaving an intiranged between 9 and 12 mils in thickness. The films were mate dispersion of stabilizer in the polymer. cut into samples having a width of 1 centimeter.

The quantity of the mercapto compound used in com- The efiect of heat aging on brittleness of the molded bination with the polyphenylene oxide in order to effect films formed from both powder blends and pellets was stabilization may vary between 0.1 and 5%, but best determined by measuring the fold number. The fold numresults are achieved when it constitutes from 2-3% of her is determined by subjecting the film strip to a series the total concentration and this constitutes a preferr d of folding cycles which comprises in folding the film embodiment of this invention. To form the benzoate of through 180 and pressing the two halves firmly together Z-mercapto benzimidazole, Z-rnercapto benzo thiazole without creasing them. Thereafter, the film is folded in or 2-benzo in situ, approximately 0.1-2% of the respeethe opposite direction through 360 to complete 1 /2 tive Z-mercapto compound is added to the polymer along cycles and then continuously refolded through 360 until with from 34% of the material capable of reacting a crease forms and /6, of the width has been ruptured. therewith to form the corresponding benzoate. The number of folding cycles required for this rupture is The polyphenylene oxides containing the stabilizers of defined as the fold number. The results of the aging tests this invention have excellent resistance to discoloration appear in Table I, below. Aging was conducted at 150 C. and em'brittlement due to oxygen attack, even after aging and 175 C. The letter B appearing in the example nos.

at elevated temperatures, for sustained periods of time. indicates a film formed from extruded pellets. Generally, For example, a film of a poly (2,6-dimethyl-1,4-phenylthe samples formed from pellets possessed poorer propene)-oxide containing the benzoate of Z-mercapto benzerties as extrusion was carried out at a temperature eximidazole dibenzoate has a fold number of 30 after ceeding 500 F. and this caused aging of the polymer. The aging 8 days at 150 C. The same polymer unstabilized numbers appearing in the columns represent fold numbers. and aged in the same manner had a fold number of less 25 The following results were obtained:

TABLE I.EFFECT OF HEAT AGING AT 150 C. AND 175 C. ON BRITTLENESS OF POLYPHENYLENE OXIDE Fold Number Ex. No. Composition (Additive and Percent) 150 C. (Days) 175 C. (Hours) 2 0 0 0 3 do 6 3 1. 0% 2-mercapto benzirnidazole. 4.. 1.0% 2-mercaptobenzothiazoleu 8 5.. .1%2-mereaptobenzothlazole 7 6 1% 2-mercapto benzimidazoie dibenzoate-- 7 1% Z-mercapto benzothiazole benzoate 7E do 8 1% 2d mercapt-o benzimidazole, 1%

am 9 1% 2-mereapto bcnzimidazole, 2% benzoic 19 0 10 anhydrido. 10 do 15 0 9 11 2% Z-rnereapto banzimidazole, 4% benzoic 30 8 angiydride.

2-morcapto benzimidazole dibanzoate. 2% 27 7 benlzoic anhydride, 2% 2-rnercapto bonzimid- {1Z0 6. 13E 2% 2-mercapto benzimidazole dibenzaote, 2% 6 benzoio anliydrida. 14 2%2-rnorcn'pto benzimidazole, 2% benzoic 30 2 1O 10 anhydride, 1% benzoic acid. 15 2% 2-mercapto oxazole benzoate 15 4 0 than 1. In addition, the stabilized sample possessed a From the above, it is apparent that addition of stavery pale yellow coloration after aging while the unstabilizer substantially increases the fold number. A combilized polymer appeared dark brown. This improvement parison of Examples l5 with the remaining examples in stability is particularly surprising as a Z-mercaPt illustrates the improvement that may be obtained using benzimidazole when used with the same polyphenylene the stabilizer system of the present invention over the oxide aged 8 days at 150 C. had a fold number of only prior art stabilizers. 8 and possessed a dark yellow coloration.

The following examples are set forth for purposes of Examples 16 26 illustration only and are not to be construed as limiting. The films formed from the powder blends and pellets All percentages expressed in the examples are by weight (10 of the above examples were used to determine the effect unless indicated otherwise. of aging at temperatures of 150 C. and 175 C. on color of the polymer. Samples of films pressed from powder and pellet were periodically examined after prolonged ex- Stabilized samples were prepared from a p0 y-(2,6- posure to high temperatures in the presence of oxygen im y -p eny1ene)-oxide having an intrinsic V O and a visual determination of color observed. The results ity of approximately 0.50 deciliters per gram (dL/g.) as are set forth in Table 11 below. For brevity, the following Examples 1-5 measured in ChlOIOfOIIIl at 111 all fiases, Samples symbols were used to represent the color of the film: were prepared by mixing 250 grams of the polyphenyiene oxide in powder form with the appropriate quantity C-colorless or very pale yellow of stabilizer in a blender to form a dry blend. After L-Light blending for a period of 1-2 minutes, a portion of the DDark dry blend was passed through an extruder and the ex- G-Green truded strand was chopped into pellets. Thereafter, films YYellow were molded from both the powder blend and the pellets. Br--Brown The films were formed by placing the polymer between BlBlack TABLE II.-EFFECT OF HEAT AGING ON COLOR OF POLYIHENYLENE OXIDE AT 150 C. AND 175 0.

150 C. (days) 175 0. (hours) Ex. No. Composition (Additive and Percent) DY Br Br LBr DBr Br Br Br Dy Br Dy Dy acid. 1% ggnercapto benzimidazole, 2% benzolc LY Y Br Br aci 22 1% 2-mercapto benzimidazolo, 2% benzoic Y anhydrlde. 23 1% 2-mereapto benzimidazole, 4% benzoic LY LY anhydride. 23E .do. LY LY LY LY 24 2% 2-mercapto benzimidazole, 2% benzoic anhydride. 24E do Y 25 2% 2-mercapto benzimidazole, 1% benzoie 0 acid, 1% benzoie anhydride. 25E .do G 26 2% Z-mercapto benzimidazole, 2% 2-mer- C capto benzimidazole, dibenzoate 2% benzoic anhydrlde.

Example 27 consisting of hydrogen and a benzoyl radical of the Following the procedures of the a'boxe examples, a sample was prepared from a poly-(2-methyl-6-phenyl- 1,4-phenylene) oxide having an intrinsic viscosity of 0.98 dL/g. as measured in chloroform at 30 C. The sample contained 2% 2-mercapto benzimidazole dibenzoate. The sample was aged in air for 120 hours at 175 C. It has a yellow coloration. A sample of the same polymer without stabilizer was dark brown after the same aging procedure. The stabilized sample had a fold number of A while the standard was too brittle to measure.

It should, of course, be apparent to those skilled in the art that changes may be made in the particular emmodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An oxidation resistant polyphenylene oxide having at least one aliphatic side chain attached to a phenylene nucleus stabilized with from 0.1 to 5.0% by weight of a compound having the formula where a is a whole number equal to 0 or 1; Z is a member selected from the group consisting of oxygen, nitrogen and sulfur; R is a member selected from the group formula where R" is a member selected from the group consisting of hydrogen and an alkyl group having from 1-3 carbon atoms and b is a whole number equal to from 0 t0 the number of replaceable hydrogen atoms on the phenylene nucleus; provided that at least one of said Rs be a benzoyl radical and provided further that when Z is sulfur or oxygen, a is 0.

2. The composition of claim 1 wherein the stabilizer comprises from 2 t0 3% by weight of the total composition.

3. The composition of claim 2 wherein the polyphenylene oxide is poly-(2,6-dimethyl-1,4-phenylene) oxide.

4. The composition of claim 3 wherein the stabilizer is the dibenzoate of Z-mercaptobenzimidazole.

5. The composition of claim 3 wherein the stabilizer is the benzoate of 2-rnercapto benzothiazole.

6. The composition of claim 3 wherein the stabilizer is the benzoate of 2-mercaptobenzoXaz0le. 

